The objective of these studies is to understand the role played by the central monoamine systems in the regulation of motivation in mammals, with particular emphasis given to behavior produced and maintained by electrical stimulation of the brain. Two approaches have been selected. With the first, the adrenergic innervation of the brain is permanenly altered by the use of neurotoxins such as 6-hydroxydopamine and 5,6-dihydroxy-tryptamine to test for effects of this change on positively motivated behavior. The behavioral experiments are carried out in adult rats when the processes of dengeneration and regeneration have stabilized. Particular emphasis is given to rewarding brain stimulated behavior, maintained by electrical stimulation of the hindbrain, to test for the effects of "sprouting" produced in the proximity of catecholamine-containing perikarya. We have already obtained evidence of a positive correlation between high rates of responding for brain stimulation in the region of the locus coeruleus and elevated norepinephrine levels in this same region in animals treated neonatally with 6-hydroxydopamine. With the second approach, the developmental aspects of brain-stimulated behavior are correlated with the developmental aspects of central catecholamine systems. Our results from the second set of studies indicate the presence of stimulation-induced rewarding properties in hypothalamus in 20-26-day-old rats and this is correlated with the presence of catecholamines in the region stimulated as shown by fluorescence of catecholamine neural elements. The first set of experiments are thus expected to shed light on the relationship between low or high levels of catecholamines in structures containing catecholamine cells bodies and brain stimulated behavior; the second set of experiments should indicate the necessity of the catecholamine systems being fully functional before brain stimulated rewarded behavior can be obtained.